It is very important to cite your sources for at least a couple of reasons:
  1. Acknowledge the words and works of others from whom you are learning.
  2. Make it possible for yourself and others who might be interested to locate the source again.

There are several different citation styles and the one to use depends on which teacher/professor you have, which area of study you go into, etc.
So, rather than give you strict guidelines that I will police, I will give a list of things that should be included:
  • Name of the person who said/wrote the information
  • Name of the book or other media where you found it
  • Author of the book, if different from the person who said/wrote it
  • Page in the book where the info can be found
  • URL if the item is found online

Information that needs to be collected for a full citation generally includes:
  • Publisher name, location, and date
  • The date you accessed an online article or website

Citation Machine is an online tool that builds the citation for you in any of several formats.